The advantages of controlled release products are well known in the pharmaceutical field and include the ability to maintain a desired blood level of a medicament over a comparatively longer period of time while increasing patient compliance by reducing the number of administrations necessary to achieve the same. These advantages have been attained by a wide variety of methods. For example, different hydrogels have been described for use in controlled release medicines, some of which are synthetic, but most of which are semi-synthetic or of natural origin. A few contain both synthetic and non-synthetic material. However, some of the systems require special process and production equipment, and in addition some of these systems are susceptible to variable drug release.
Oral controlled release delivery systems should ideally be adaptable so that release rates and profiles can be matched to physiological and chronotherapeutic requirements. While many controlled and sustained release formulations are already known, certain moderately to poorly soluble drugs present formulation difficulties which render them inapplicable for sustained release formulations which might be suitable for, e.g., relatively soluble drugs. It is often not possible to readily predict whether a particular sustained release formulation will provide the desired sustained release for a relatively insoluble drug, and it has generally been found that it is necessary to carry out considerable experimentation to obtain sustained release formulations of such drugs having the desired bioavailability when ingested, particularly for drugs that are poorly soluble in water.
An example of a poorly soluble drug is nifedipine. Nifedipine often exhibits poor bioavailability when incorporated into sustained release formulations. Accordingly, a great deal of attention has been given to the preparation of sustained release nifedipine formulations which provide acceptable bioavailability. U.S. Pat. No. 4,765,989 (Wong, et al.) describes an osmotic system wherein nifedipine is contained along with osmopolymers in a compartment enclosed by a wall which is substantially impermeable to the passage of tile drug. The osmopolymer exhibits an osmotic pressure gradient across the wall against the external fluid. A passageway in the wall communicates with the first composition and the exterior of the device for delivering nifedipine to the passageway.
Other techniques which have been described for preparing sustained release nifedipine formulations include the transformation of crystalline nifedipine into fine powder, the transformation of the crystalline nifedipine to the amorphous form, the formation of clathrates or compounds of inclusion with betacyclodextrines, and the formation of solid solutions with polyethylene glycols ("PEGs").
Still other techniques are directed to processes for increasing the bioavailability of nifedipine. U.S. Pat. No. 4,880,623 (Piergiorgio, et al.) describes a process wherein nifedipine and polyethylene glycol are coprecipitated from a solution into a product in the form of very fine particles having an extremely high total specific surface. In one embodiment, substances which swell upon contact with the gastrointestinal juices and successively dissolve slowly (selected from hydroxypropylmethyl cellulose, methyl cellulose, hydroxypropyl cellulose, carboxyvinyl polymers, xanthan gum) in quantities from 5-50% of the tablet are added so as to obtain the prolongation of the retard effect.
Falk, et al., U.S. Pat. No. 4,803,081, describes compositions and processes for preparing controlled release formulations that include low solubility active ingredients, such as nifedipine, dissolved in a liquid or semi-solid solubilizing agent and further in a controlled release system that does not include locust bean gum.
Mulligan et al., in U.S. Pat. Nos. 4,973,469 and 5,128,142 (assigned to the Elan Corporation) describes compositions and processes for preparing controlled release formulations that include an adsorbate prepared from a mixture of a pharmaceutically useful active ingredient, e.g., nifedipine, and an inactive substance adsorbed on a cross-linked polymer. The formation of the adsorbate is stated to render the active ingredient into an amorphous form. The inactive substance can be, e.g., water insoluble polymers such as polyvinyl alcohol, polyvinylpyrrolidone and hydroxyethylcelluose.
Rhodes in U.S. Pat. No. 5,145,683 (assigned to Ethical Pharmaceuticals, Ltd.) describes amorphous nifedipine prepared as finely divided particles of 100 microns or less as a composition that includes polyvinylpyrrolidone (PVP) in a weight ratio of 10 to 90 percent relative to the weight of nifedipine. Nifedipine coated carrier particles are prepared by mixing nifedipine with polyvinylpyrrolidone and acrylic-based polymer in a solvent, e.g., ethanol. The mixture is then coated onto a water soluble carrier followed by evaporation of the solvent to provide what is asserted to be an amorphous nifedipine coating of water soluble carrier particles.
Hegasy et al. in U.S. Pat. No. 4,562,069 (assigned to Bayer Aktiengesellschaft) discloses formulations including combinations of crystalline and non-crystalline nifedipine. The Hegasy dosage form is described as a "two-phase" formulation including a nifedipine coprecipitate in which the nifedipine is present in both a crystalline and noncrystalline form. The Hegasy formulation is prepared by dissolving nifedipine and the coprecipitate (e.g., PVP, methylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose) in a suitable organic solvent (e.g., ethanol) and the remaining solid precipitation is comminuted.
Previously, heterodisperse polysaccharide excipient systems and controlled release oral solid dosage forms were described in U.S. Pat. Nos. 4,994,276, 5,128,143, and 5,135,757. These systems are commercially available under the tradename TIMERx.TM. from Edward Mendell Co., Inc., Patterson, N.Y., which is the assignee of the present invention. These patents are hereby incorporated by reference.